The present invention relates to the field of devices for photocatalytic treatment of fluids, for instance for cleaning, deodorizing and sterilizing gases such as air.
Numerous air purification systems have been described, or are commercially available, which aim to remove various pollutants, such as dust, micro-particles, noxious gases, allergens, and pathogenic micro-organisms from the air. In the known systems, dust and other micro-particles are generally removed from the air by the use of filters. It is known to remove certain volatile and reactive molecules by the use of catalytic processes. The use of ultraviolet light radiation to inactivate certain micro-organisms is also described. It is known to combine the use of ultraviolet light and photocatalytic processes to accelerate the degradation of noxious particles and the destruction of micro-organisms.
The use of photocatalysts in devices for deodorising or purifying air is described in a number of patent applications, for example, U.S. Pat. No. 5,670,126, U.S. Pat. No. 6,558,639, US 2002/094298, U.S. Pat. No. 6,358,374, US 2004/007453, JP 11226357, WO 02/085989, and FR 2821558. The most common photocatalytic compound used in the known systems is titanium dioxide because of its excellent photocatalytic activity when irradiated with ultraviolet radiation, and its harmlessness to the human organism.
The photocatalyst is generally combined with a binder to form a photocatytic coating material. A photocatalytic material which is convenient to use, adheres well to a number of surface and may be applied to articles which do not support high temperatures is described in WO 2006/010993, hereby incorporated herein by reference. The photocatalytic material described in WO 2006/010993 comprises an inorganic binder including ultraviolet light permeable polymeric molecules, particularly acrylic molecules, a polar diluent, and particles of an inorganic semi-conductor, such as cadmium sulphide, zinc sulphide or titanium dioxide.
In known systems the photocatalytic material is generally coated on a filter element or other surfaces of the air purifying system irradiated by an ultraviolet light source, typically an ultraviolet lamp. For example EP 0978690 and WO 96/37281 describe systems in which air is passed through an air-permeable sheet supporting a photocatalytic material and placed in the vicinity of an ultraviolet light source. Such systems generally provide only limited air cleaning properties with respect to removing certain airborne pollutants, allergens and pathogens.
A system with improved air cleaning properties is described by WO 2007/060520, in which a photocatalytic material is coated on an inside surface of a tubular air conduit containing a UV lamp. A number of spaced apart blades are located on the inside surface of the air conduit in order to increase the surface area of photocatalytic material in the air conduit and to create turbulent flow of the air through the conduit.
EP 0470518 describes a system designed for the decomposition of organic substances in which a liquid is passed through a stainless steel reaction vessel containing an ultraviolet immersion lamp. According to EP 0470518 baffles are located on the inner surface of the stainless steel tube to cause turbulence in the flow of the liquid on the reaction vessel inner surface.
The known systems do however present a number of drawbacks. For instance the known systems are generally relatively complex and costly to manufacture and/or maintain. Moreover, the known systems either do not effectively treat all the air passing through the device, and/or cause excessive resistance on the air passing through with the consequence of increased noise and the need to employ more powerful fans for a given rate of airflow.
There is also an ongoing need for air purification systems which reliably and effectively remove, destroy or inactivate airborne pollutants, allergens and pathogens.